The present invention relates to a method for the production of injection-moulded, reinforced moulded parts, the fibre orientation of which is specifically adjusted on a local basis. Via suitable, dynamically controlled supplementary heating in the wall of the injection mould which is used (variotherm heatable channel), a local cavity region is hereby heated at the time of injection to a temperature in the region of or above the solidification temperature (in any case above the crystallisation temperature in the case of partially crystalline plastic materials or above the glass transition temperature in the case of amorphous plastic materials) of the polymer (plastic material moulding compound).
In conventional injection moulding, a plastic material melt is injected into a temperature-controlled mould, the mould wall temperature of which is normally below the solidification temperature for the respective plastic material (crystallisation temperature in the case of partially crystalline plastic materials or the glass transition temperature in the case of amorphous plastic materials). The core of the melt front thereby remains flowable and the plastic material is driven forwards in the cavity by the injection pressure, whilst the edge zones in the vicinity of the mould wall rapidly cool down and solidify. If the mould cavity is filled and the plastic material is completely solidified, the moulded part is released from the mould. Over the entire injection-moulding cycle, the mould wall is kept at the same temperature. The mould temperature-control can hence be understood as cooling in order to dissipate the heat energy of the melt, including any possible crystallisation heat, which is introduced into the mould during each injection.
In the case of long flow paths and simultaneously thin wall thicknesses, this can lead to freezing of the cross-section and hence prevent complete filling of the cavity. Furthermore, structured and high-gloss surfaces are not completely reproduced. In addition, if flow fronts flow together, the result is formation of visible joint lines.
The so-called variotherm mould temperature-control offers a remedy for the above-mentioned problems. Via supplementary heating, the cavity is heated up at the time of injection to the level of the melt temperature (at least above the crystallisation temperature) of the partially crystalline plastic material (or glass transition temperature in the case of amorphous plastic materials) and, after completion of the mould filling, it is cooled down to temperatures significantly below the solidification temperature. Heating of the mould wall is hereby effected essentially over the entire surface and hence uniformly. As a result of the higher melt- and mould temperature which can be achieved with this method during injection moulding, the viscosity of the polymer melt is significantly reduced and the moulding of problematic parts is improved or made possible at all. The temperature changes must thereby be effected as rapidly as possible in order that an adequate productivity can be ensured.
The advantages of variotherm mould temperature-control are:                less distortion and deformations of the components        formation of high-gloss surfaces, even with foamed plastic materials        avoidance of fibre traces on the surface of the moulded parts        moulding of thin-walled components possible        reducing the cycle times in the case of thick-walled components        higher homogeneity and hence greater strengths        no visible joint lines        
In this type of variotherm mould temperature-control, the entire cavity (mould wall) is heated up or cooled down during the injection-moulding cycle. In the case of non-reinforced moulding compounds, a definite improvement in the joint line strength can be ascertained If, in contrast, reinforced moulding compounds, which include for example carbon- or glass fibres as reinforcing fibres, are injected, the fibre orientation does not change with variotherm mould temperature-control relative to conventional injection moulding methods since the fibre orientation is defined primarily by the gate location and the flow paths resulting therefrom. Hence, in fact some joint lines disappear visually from the surface of the moulded part but not from the moulded part itself. Since the strength of the moulded part based on reinforced moulding compounds is dominated by the fibre orientation, the joint line strength is hence in no way improved.
It is therefore the object of the present invention to provide a new injection moulding method which can adjust the orientation of reinforcing fibres within a plastic material melt in a defined manner by means of a locally limited, variotherm mould temperature-control and hence the strength in the principal loading direction (direction of the principal stress) of the moulded part is improved.
In addition, it is the object of the present invention to indicate a corresponding moulded part in which specific alignment of the orientation of the contained fibres is present. A further object of the present invention is to provide a corresponding injection mould for the production of a moulded part according to the invention or for implementing a method according to the invention.